It may be recalled that, with such electron multiplier devices of the type described, an electric field is produced in the channel by establishing a suitable potential difference between the extremities and by causing a beam of primary electrons to penetrate into the channel under difficult angles thereby resulting in a series of secondary electron emissions on the internal wall of the channel. At the output, the number of electrons is greatly increased as compared to the primary beam at the input. An electron multiplier device can be used in the form of a single tube, or a plurality of such tubes can be bundled together.
Typical prior art secondary electron multipliers consist of straight or curved tubes of insulating material, such as glass, coated on its entire inside surface with a conductive coating made of secondary electron emissive material. There exists also another type of secondary electron multiplier using a tube made only of ceramic such as barium titanate or zinc titanate which may be found described in U.S. Pat. No. 3,612,946 issued Oct. 12, 1971 to Toyoda.
While the ceramic type of electron multiplier devices overcome the many disadvantages associated with electron multiplier devices wherein the insulating material used is glass (little resistance to impact the charged particles or mechanical injuries, expensive to mass produce, unstable in operation, etc.), they are, however, limited in construction and in use. Indeed, since the ceramic materials used in these electron multiplier devices have semi-conducting properties, it is practically impossible to maintain a uniform potential gradient inside a curved channel machined or molded in a bulk piece of semi-conducting ceramic. The polarising current in semi-conducting ceramic electron multiplier is distributed inside the whole body of the multiplier this characteristic imposes a limitation on their construction. For such multipliers to operate satisfactorily, the thickness of the ceramic must be constant throughout the length of the multiplier channel. The selection of ceramic to be used is extremely limited and as described in the above mentioned Toyoda patent, the advantages obtained with ceramic is best achieved with a barium titanate or zinc titanate family semi-conducting ceramic material having positive or zero-resistance temperature characteristics. Such ceramic is not one which is easily machinable or moldable with high accuracy thereby limiting the shapes which can be given to an electron multiplier device.